Spring means for roller mills and the like



Dec. 10, 1957 ,'c s 2,815,903

SPRING MEANS FOR ROLLER MILLS AND THE LIKE Filed Noir. 1, 1951 V 2 Sheets-Sheet 1 Feed Tub'8\ l I 5;; Offfuke ca I I v A I v 2' INVENTOR Dec. 10, 195.7

J. CRITES SPRING MEANS, F'oRlRoLLER MILLS AND THE LIKE 2 Sheets-Sheet 2 Filed Nov. 1, 1951 m E a E INVENTOR Joe Grites QaE L-L ATTOR EY United States Patent SPRING MEANS FOR ROLLER MILLS AND THE LIKE Joe Crites, Larchmont, N. Y., assignor to Combustion Engineering, Inc., a corporation of Delaware Application November 1, H51, Serial N 0. 254,287 Claims. (Cl. 241118) This invention relates to roller mills and the like and particularly to improved spring means for maintaining pressures between the rolls and the grinding member (grinding ring, bowl, table or the like) cooperating therewith.

In roller type mills as constructed heretofore the spring (or springs) which maintains the pressure between the roll and the grinding member acts upon one end of an arm which is journaled near its mid point, while the roll for engaging the grinding member is journaled on the other end of said arm. Said one end of the arm has an adjustable stop on the side opposite to the spring, which stop serves to limit the movement of the arm and the spring and to space the roll from the grinding ring by a predetermined clearance when no material passes therebetween. The spring being under an initial compression when the arm is against the stop, prevents the roll from moving toward or bearing against the grinding nng.

The resultant advantage of so spacing the roll from the grinding ring is a quiet running mill, because there is never a metal-to-metal contact of the grinding elements. However, this clearance has proven a disadvantage when the mill is starting up in that there is no friction between the roll and the grinding ring to start the roll rotating. When the roll and the' ring are new this clearance (which typically may be about inch) is not objectionable because the material to be ground which is fed to the mill offers enough friction between the surfaces of the roll and ring to start the roll rotating. But when the roll and ring are badly worn, said clearance may be as much as 1 /2 inches at certain portions of the roll; and When such clearances occur the roll will not start rotating unless means are resorted to such as feeding rocks into the mill. The roll passing over the rocks will usually start it rotating.

5 Generally stated, the object of my invention is to overcome the starting difficulty just mentioned.

A more specific object is to provide improved spring means, in mills employing grinding rolls, which will permit the roll and grinding ring, when the mill is empty, to engage in rotating contact with but a relatively small pressure therebetween.

Other objects and advantages of the invention will become apparent from the following description of an illustrative embodiment thereof when taken in conjunction with the accompanying drawings, wherein Fig; 1 is a cross section in elevation of a bowl mill type of roller mill with a portion of the casing broken away to show interiorly a typical roll and exteriorl'y that rolls associated improved spring means embodying the invention;

Figs. 2 and 3 are respective sectional side and front elevations of the improved spring means taken on lines 2-2 and 3-3 of Figs. 3 and 2 respectively.

Referring to Fig. 1, a roller mill generally designated as M is here shown by way of example as of the well known Bow1- type. This illustrative mill comprises a base 1 supporting a casing 22' thereabove Within the lower portion 2 of which is a bowl 3 mounted for rotation about a vertical shaft 4. The shaft 4 is supported in bearings (not shown) mounted within the base 1 and is rotated by a system of bevel gears (also not shown) within the base I. Said gears are in turn driven by a motor 5 through shaft 6.

The bowl 3 contains a peripheral grinding ring 7 onto which the material to be ground flows by centrifugal force from the inner portion of the rotating bowl. The material to be ground is supplied to the bowl downwardly from the mill top through a central feed tube 8 from which it passes further downwardly from the upper casing portion 2' through opening 9 into the bowl 3. The rotation of the bowl causes the material to flow outwardly onto the ring 7 to the rolls 10 where it is ground in passing between the rolls 10 and the ring 7.

An air current flows in well known manner upwardly between the rim of bowl 3 and the surrounding casing 2 and carries the sufiiciently ground material up through the mill, as shown by the arrows, and out through the top olftake 11. The insufficiently ground material is separated out of the air stream by the represented classifier 12 and falls back into the bowl 3 through opening 9 to be further ground.

The particular bowl here shown is equipped with three rolls 10 (only two can be seen in Fig. 1). Each roll 10 is mounted to freely rotate about the lower end of a shaft 13 which shaft is fastened at its upper end to an arm 14. Arm 14 is mounted to freely rotate on trunnion 15 which is carried in bearings 16, one of which is shown in cross section, mounted on the cover 17 of casing 2. Arm 14 extends radially outwardly of the mill and terminates in a head 18 beyond the outer edge of cover 17.

In the arrangement illustrated by Fig. l the roller 10 is urged towards grinding ring 7 by a main spring 19 which exerts an upward force on the outer or free end of arm 14. As shown in detail in Figs. 2 and 3, this main pressure spring 19 derives support from members 20 that extend radially from the cover 17 on either side of the spring, each of said members 20 being slotted to receive one of two vertical bolts 21 which are fully threaded and fastened to the members 20 by top and bottom nuts 22. A yoke 23 straddles the bolts 21 at their lower ends, is supported by nuts 24 on said bolts, and forms a spring seat 25 against which the lower end of the main pressure spring 19 bears.

A spring adjustment stud 26 passes freely through the 0 spring seat 25 of yoke 23 and thence upwardly axially through the spring 19. At the top of the threaded stud 26 is a nut 27 (with lock nut) flanged to receive the top of the spring 19 as shown. At the bottom of the threaded stud 26 are nuts 28 by which the spring 19 may be compressed to the desired loading. After the spring has been compressed, the spring assembly including spring 19, stud 26, nut 27 and yoke 23 may be raised or lowered with respect to the members 20 on cover 17 by means of adjusting nuts 22.

According to the invention the main spring 19 is limited in its upward movement by the spring adjusting stud 26, and the upper face of nut 27 is spaced from the lower surface 29 of the head 18 of the journal arm 14 by a gap 30. When this gap 39 is present, there is no material being ground and the arm 14 has rotated clockwise on trunnion 15 due to the weight of the roll, until the roll 10 contacts the ring 7. The roll 10 is now free to move away from the ring 7 a distance that is limited by 0 the gap 30-.

The roll 10 now touches the ring 7 and starts rolling thereon when starting up the mill. The pressure on the this relatively slight pressure is not enough to cause any undue vibration. When the roll is moved away from ring 7 by the material being ground therebetween, beyond the distance permitted by the gap 30, the surface 29 of the head 18 of arm 14 contacts the nut 27 of spring 19.

Any further movement of the roll 10 away from ring 7 is resisted by the compression of spring 19 and efiects the grinding of the material in the usual manner.

While I have here disclosed my invention as being applied to a bowl-type mill having rolls 10 urged towards a grinding ring 7 carried by a rotatable bowl 3, it will be apparent that such disclosure is illustrative rather than restrictive and that my inventive improvements may with comparable benefit also be applied to mills of other types, such as those using rollers or balls running adjacent tables or races, wherein the problem solved by this invention is encountered.

Moreover, even though only one illustrative embodiment has been shown and described, it will be understood that changes in construction, combination and arrangement of parts may be made without departing from the spirit and scope of the invention as claimed.

I claim:

1. In a roller mill having a casing, the combination of a rotatable grinding member in the casing, a roll also disposed in said casing and arranged to roll on said member for the purpose of grinding material between the member and the roll, shaft means on which said roll is mounted for rotation thereon during said grinding, a trunnion bearing mounting said shaft on said casing and permitting movement of said roll about the trunnion toward and away from said grinding member while allowing the roll to drop under gravity into gentle contact with the member in the absence of material separating the two, a coil spring arranged to be compressed between said shaft means and a support member to urge said roll toward said grinding member, said support member being positioned relative to said shaft means to relieve said shaft means of the action of said spring when the roll is within a predetermined distance of the grinding member and means engaging the end of the spring acting on the shaft means to limit the movement of this end of said spring away from said support means when said roll is within said predetermined distance to thereby pre-stress said spring and maintain a predetermined stress therein when the shaft means is relieved of the action of the spring.

2. In a roller mill having a casing, the combination of a rotatable grinding member in the casing; 21 roll also disposed in said casing and arranged to roll on said member for the purpose of grinding material between the member and the roll; shaft means on which said roll is mounted for rotation thereon during said grinding; a trunnion bearing mounting said shaft on said casing and permitting movement of said roll about the trunnion toward and away from said grinding member while allowing the roll to drop under gravity into gentle contact with the member in the absence of material separating the two; a coil spring arranged to have its one end act on said shaft means to urge said roll toward said member; a yoke supporting the other end of said spring; studs extending parallel to the axis of said spring through holes in said yoke; lugs on said casing having apertures to receive said studs and nuts on said studs bearing against both sides of said yoke and said lugs to thereby adjustably move said yoke with respect to said casing; a stud extending longitudinally through said spring and through a hole in said yoke and nuts on said stud, one of said nuts bearing against said springs one end acting as a stop to limit the expanding movement of said spring and another of said nuts bearing against the side of said yoke opposite said spring; said spring associated stud and nuts compressing said spring to a desired loading, said yoke adjustment causing said one spring end to cease acting on said shaft and therewith on said roll when said roll approaches said grinding member with a predetermined closeness whereby in starting up the mill when empty said roll bears against said grinding member with only the aforesaid gentle contact due to gravity.

3. The combination of a pulverizing mill having a grinding member and a pivotally mounted roll urged by gravity into engagement with said grinding member and movable toward and away from said grinding member, spring means including a spring urging said roll toward said grinding member, means forming a part of said spring means operable to relieve said roll of the force of said spring urging the roll toward the grinding member when said roll reaches and is within a predetermined distance of the grinding member allowing said roll to freely move toward and away from the grinding member through said predetermined distance, and means for pre-stressing said spring so that the initial bias that said spring means imparts to the roll at said predetermined distance is of a predetermined magnitude.

4. In combination with a roller type pulverizing mill having a movable grinding member, a roll and means for pivotally mounting said roll in such a manner that it is urged by gravity into engagement with the grinding member and is movable toward and away from said grinding member, spring means cooperating with said mounting means to urge said roll toward said grinding means including a coil spring adapted to be compressed against a movable portion of said mounting means, means for relieving said movable portion of the force of said spring urging said portion in the direction to move said roller toward said grinding member when said portion occupies a position corresponding to a location of the roller within a predetermined distance of the grinding member, and means providing the spring with a predetermined compression when said roll is within said predetermined distance and said spring is not effective to urge said roll toward said ring, so that said spring will provide a force of predetermined magnitude upon initially becoming elfective to urge the roll toward the grinding member.

5. In combination with a roller type pulverizing mill having a movable grinding member, a roll and means for pivotally mounting said roll for movement toward and away from said grinding member and into engagement with said grinding member through the influence of gravity, spring means cooperating with said mounting means to urge said roll toward said grinding means and including a coil spring positioned intermediate a fixed member and a movable portion of said mounting means so as to be compressed therebetween, said fixed member being positioned relative to said movable portion of the mounting means so as to prevent the spring from urging the roller toward the ring when the roller is within a predetermined distance of the grinding member and means providing the spring with a predetermined compression when said roll is within said predetermined distance and said spring is not effective to urge said roll toward said ring so that said spring will provide a force of predetermined magnitude upon initially becoming effective to urge the roll toward the ring.

References Cited in the file of this patent UNITED STATES PATENTS 652,329 Raymond June 26, 1900 791,680 Eggers June 6, 1905 940,513 Clark Nov. 16, 1909 1,360,465 Sturtevant Nov. 30, 1920 1,478,478 Kreutzberg Dec. 25, 1923 2,100,734 Crites Nov. 30, 1937 2,112,359 Crites Mar. 29, 1938 2,461,176 Piper Feb. 8, 1949 FOREIGN PATENTS 451,504 Germany Oct. 22, 1927 

